The goal of this project is to understand the distribution and functions of cytoplasmic motors in the axon of neurons. This information is intended to lead to an understanding, at the molecular level, of fast and slow axonal transport as well as the cytoplasmic organization in the axon. The central project in the Section on Structural Cell Biology, has been particularly active this year, providing a plethora of new findings. A new functional assay for myosins was introduced and used to uncover a novel class of myosin II-like motors on the surfaces of squid axonal organelles. This 235 kDa myosin is double headed and appears to adhere strongly to the surfaces of axonal organelles. The organization of the actin substrates for these motors in the axon is also under study. A possible assay useful for approaching the difficult problem of defining the mechanism of slow transport has also been introduced. Macromolecular assemblies injected into the squid giant axon move in the anterograde direction only and require ATP. Of particular interest is that short actin filaments also move anterogradely and that all movements appear to be along some type of intracellular tract. This in vitro assay may make it possible to define the motors for such movements. The bacterial flagellar motor in E. coli has been studied as another example of a motor system than can switch direction of translocation. We recently discovered a new cytoplasmic component of the flagellar motor thought to be involved in directional switching-antibodies to known switching components appear to stain this new structure.